Electricity for Boys Part 9

Now, supposing the switch (D'), in station 2, should be thrown over so it contacts with the wire (H'). It is obvious that the current will then flow from the battery (I') through wires (H', C') and line (A) to station 1; then through wire C, switch D, wire E to the bell F, to the ground through wire G. From wire G the current returns through the ground to station 2, where it flows up wire G' to the battery, thereby completing the circuit.

[Ill.u.s.tration: _Fig. 85._ ILl.u.s.tRATING LIGHT CONTACT POINTS]

The operator at station 2, having given the signal, again throws his switch (D') back to the position shown in Fig. 84, and the operator at station 1 throws on his switch (D), so as to ring the bell in station 2, thereby answering the signal, which means that both switches are again to be thrown over so they contact with the battery wires (H and H'), respectively. When both are thus thrown over, the bells (G, G') are cut out of the circuit, and the batteries are both thrown in, so that the telephones are now ready for talking purposes.

MICROPHONE.--Originally this form of telephone system was generally employed, but it was found that for long distances a more sensitive instrument was necessary.

LIGHT CONTACT POINTS.--In 1877 Professor Hughes discovered, accidentally, that a light contact point in an electric circuit augmented the sound in a telephone circuit. If, for instance, a light pin, or a nail (A, Fig. 85) should be used to connect the severed ends of a wire (B), the sounds in the telephone not only would be louder, but they would be more distinct, and the first instrument made practically, to demonstrate this, is shown in Fig. 86.

[Ill.u.s.tration: _Fig. 86._ MICROPHONE]

[Ill.u.s.tration: _Fig. 87._ TRANSMITTER]

HOW TO MAKE A MICROPHONE.--This instrument has simply a base (A) of wood, and near one end is a perpendicular sounding-board (B) of wood, to one side of which is attached, by wax or otherwise, a pair of carbon blocks (C, D). The lower carbon block (C) has a cup-shaped depression in its upper side, and the upper block has a similar depression in its lower side. A carbon pencil (E) is lightly held within these cups, so that the lightest contact of the upper end of the pencil with the carbon block, makes the instrument so sensitive that a fly, walking upon the sounding-board, may be distinctly heard through the telephone which is in the circuit.

MICROPHONE THE FATHER OF THE TRANSMITTER.--This instrument has been greatly modified, and is now used as a transmitter, the latter thereby taking the place of the pin (A), shown in Fig. 85.

AUTOMATIC CUT-OUTS FOR TELEPHONES.--In the operation of the telephone, the great drawback originally was in inducing users of the lines to replace or adjust their instruments carefully. When switches were used, they would forget to throw them back, and all sorts of trouble resulted.

It was found necessary to provide an automatic means for throwing in and cutting out an instrument, this being done by hanging the telephone on the hook, so that the act merely of leaving the telephone made it necessary, in replacing the instrument, to cut out the apparatus.

Before describing the circuiting required for these improvements, we show, in Fig. 87, a section of a transmitter.

A cup-shaped case (A) is provided, made of some insulating material, which has a diaphragm (B) secured at its open side. This diaphragm carries the carbon pencil (C) on one side and from the blocks which support the carbon pencil the wires run to binding posts on the case.

Of course the carbon supporting posts must be insulated from each other, so the current will go through the carbon pencil (C).

COMPLETE CIRCUITING WITH TRANSMITTER.--In showing the circuiting (Fig.

88) it will not be possible to ill.u.s.trate the boxes, or casings, which receive the various instruments. For instance, the hook which carries the telephone or the receiver, is hinged within the transmitter box. The circuiting is all that it is intended to show.

[Ill.u.s.tration: _Fig. 88._ COMPLETE TELEPHONIC CIRCUIT]

The batteries of the two stations are connected up by a wire (A), unless a ground circuit is used. The other side of each battery has a wire connection (B, B') with one terminal of the transmitter, and the other terminal of the transmitter has a wire (C, C') which goes to the receiver. From the other terminal of the receiver is a wire (D, D') which leads to the upper stop contact (E, E') of the telephone hook. A wire (F, F') from the lower stop contact (G, G') of the hook goes to one terminal of the bell, and from the other terminal of the bell is a wire (H, H') which makes connection with the line wire (A). In order to make a complete circuit between the two stations, a line wire (I) is run from the pivot of the hook in station 1 to the pivot of the hook in station 2.

In the diagram, it is a.s.sumed that the receivers are on the hooks, and that both hooks are, therefore, in circuit with the lower contacts (G, G'), so that the transmitter and receiver are both out of circuit with the batteries, and the bell in circuit; but the moment the receiver, for instance, in station 1 is taken off the hook, the latter springs up so that it contacts with the stop (E), thus establishing a circuit through the line wire (I) to the hook of station 2, and from the hook through line (F') to the bell. From the bell, the line (A) carries the current back to the battery of station (A), thence through the wire (B) to the transmitter wire (C) to receiver and wire (D) to the post (E), thereby completing the circuit.

When, at station 2, the receiver is taken off the hook, and the latter contacts with the post (E'), the transmitter and receiver of both stations are in circuit with each other, but both bells are cut out.

CHAPTER XIII

ELECTROLYSIS, WATER PURIFICATION, ELECTROPLATING

DECOMPOSING LIQUIDS.--During the earlier experiments in the field of electricity, after the battery or cell was discovered, it was noted that when a current was formed in the cell, the electrolyte was charged and gases evolved from it. A similar action takes place when a current of electricity pa.s.ses through a liquid, with the result that the liquid is decomposed--that is, the liquid is broken up into its original compounds. Thus, water is composed of two parts, by bulk, of hydrogen and of oxygen, so that if two electrodes are placed in water, and a current is sent through the electrodes in either direction, all the water will finally disappear in the form of hydrogen and oxygen gases.

MAKING HYDROGEN AND OXYGEN.--During this electrical action, the hydrogen is set free at the negative pole and the oxygen at the positive pole. A simple apparatus, which any boy can make, to generate pure oxygen and pure hydrogen, is shown in Fig. 89.

It is constructed of a gla.s.s or earthen jar (A), preferably square, to which is fitted a wooden top (B), this top being provided with a packing ring (C), so as to make it air-tight. Within is a vertical part.i.tion (D), the edges of which, below the cap, fit tightly against the inner walls of the jar. This part.i.tion extends down into the jar a sufficient distance so it will terminate below the water level. A pipe is fitted through the top on each side of the part.i.tion, and each pipe has a valve. An electrode, of any convenient metal, is secured at its upper end to the top of the cap, on each side of the part.i.tion. These electrodes extend down to the bottom of the jar, and an electric wire connects with each of them at the top.

[Ill.u.s.tration: _Fig. 89._ DEVICE FOR MAKING HYDROGEN AND OXYGEN]

If a current of electricity is pa.s.sed through the wires and the electrodes, in the direction shown by the darts, hydrogen will form at the negative pole, and oxygen at the positive pole. These gases will escape upwardly, so that they will be trapped in their respective compartments, and may be drawn off by means of the pipes.

PURIFYING WATER.--Advantage is taken of this electrolytic action, to purify water. Oxygen is the most wonderful chemical in nature. It is called the acid-maker of the universe. The name is derived from two words, _oxy_ and _gen_; one denoting oxydation, and the other that it generates. In other words, it is the _generator of oxides_. It is the element which, when united with any other element, produces an acid, an alkali or a neutral compound.

RUST.--For instance, iron is largely composed of ferric acid. When oxygen, in a free or gaseous state, comes into contact with iron, it produces ferrous oxide, which is recognized as rust.

OXYGEN AS A PURIFIER.--But oxygen is also a purifier. All low forms of animal life, like bacteria or germs in water, succ.u.mb to free oxygen. By _free oxygen_ is meant oxygen in the form of gas.

COMPOSITION OF WATER.--Now, water, in which harmful germs live, is one-third oxygen. Nevertheless, the germs thrive in water, because the oxygen is in a compound state, and, therefore, not an active agent. But if oxygen, in the form of gas, can be forced through water, it will attack the germs, and destroy them.

COMMON AIR NOT A GOOD PURIFIER.--Water may be purified, to a certain extent, by forcing common air through it, and the foulest water, if run over rocks, will be purified, in a measure, because air is intermingled with it. But common air is composed of four-fifths nitrogen, and only one-fifth oxygen, and, as nitrogen is the staple article of food for bacteria, the purifying method by air is not effectual.

PURE OXYGEN.--When, however, oxygen is generated from water, by means of electrolysis, it is pure; hence is more active and is not tainted by a life-giving substance for germs, such as nitrogen.

The mechanism usually employed for purifying water is shown in Fig. 90.

A WATER PURIFIER.--The case (A, Fig. 90) may be made of metal or of an insulating material. If made of metal it must be insulated within with slate, gla.s.s, marble or hard rubber, as shown at B. The case is provided with exterior f.l.a.n.g.es (C, D), with upper and lower ends, and it is mounted upon a base plate (E) and affixed thereto by bolts. The upper end has a conically-formed cap (F) bolted to the f.l.a.n.g.es (C), and this has an outlet to which a pipe (G) is attached. The water inlet pipe (H) pa.s.ses through the lower end of the case (A). The electrodes (I, J) are secured, vertically, within the case, separated from each other equidistant, each alternate electrode being connected up with one wire (K), and the alternate electrodes with a wire (L).

[Ill.u.s.tration: _Fig. 90._ ELECTRIC WATER PURIFIER]

When the water pa.s.ses upwardly, the decomposed or gaseous oxygen percolates through the water and thus attacks the germs and destroys them.

THE USE OF HYDROGEN IN PURIFICATION.--On the other hand, the hydrogen also plays an important part in purifying the water. This depends upon the material of which the electrodes are made. Aluminum is by far the best material, as it is one of nature's most active purifiers. All clay contains aluminum, in what is known as the sulphate form, and water pa.s.sing through the clay of the earth thereby becomes purified, because of this element.

ALUMINUM ELECTRODES.--When this material is used as the electrodes in water, hydrate of aluminum is formed, or a compound of hydrogen and oxygen with aluminum. The product of decomposition is a flocculent matter which moves upwardly through the water, giving it a milky appearance. This substance is like gelatine, so that it entangles or enmeshes the germ life and prevents it from pa.s.sing through a filter.

If no filter is used, this flocculent matter, as soon as it has given off the gases, will settle to the bottom and carry with it all decomposed matter, such as germs and other organic matter attacked by the oxygen, which has become entangled in the aluminum hydrate.

ELECTRIC HAND PURIFIER.--An interesting and serviceable little purifier may be made by any boy with the simplest tools, by cutting out three pieces of sheet aluminum. Hard rolled is best for the purpose. It is better to have one of the sheets (A), the middle one, thicker than the two outer plates (B).

[Ill.u.s.tration: _Fig. 91._ PORTABLE ELECTRIC PURIFIER]

Let each sheet be 1-1/2 inches wide and 5-1/2 inches thick. One-half inch from the upper ends of the two outside plates (B, B) bore bolt holes (C), each of these holes being a quarter of an inch from the edge of the plate. The inside plate (A) has two large holes (D) corresponding with the small holes (C) in the outside plates. At the upper end of this plate form a wing (E), 1/2 inch wide and 1/2 inch long, provided with a small hole for a bolt. Next cut out two hard-rubber blocks (F), each 1-1/2 inches long, 1 inch wide and 3/8 inch thick, and then bore a hole (G) through each, corresponding with the small holes (C) in the plates (B). The machine is now ready to be a.s.sembled. If the inner plate is 1/8 inch thick and the outer plates each 1/16 inch thick, use two small eighth-inch bolts 1-1/4 inches long, and clamp together the three plates with these bolts. One of the bolts may be used to attach thereto one of the electric wires (H), and the other wire (I) is attached by a bolt to the wing (E).

[Ill.u.s.tration: _Figs. 92-95._ DETAILS OF PORTABLE PURIFIER]

Such a device will answer for a 110-volt circuit, in ordinary water. Now fill a gla.s.s nearly full of water, and stand the purifier in the gla.s.s.

Within a few minutes the action of electrolysis will be apparent by the formation of numerous bubbles on the plates, followed by the decomposition of the organic matter in the water. At first the flocculent decomposed matter will rise to the surface of the water, but before many minutes it will settle to the bottom of the gla.s.s and leave clear water above.

PURIFICATION AND SEPARATION OF METALS.--This electrolytic action is utilized in metallurgy for the purpose of producing pure metals, but it is more largely used to separate copper from its base. In order to utilize a current for this purpose, a high ampere flow and low voltage are required. The sheets of copper, containing all of its impurities, are placed within a tank, parallel with a thin copper sheet. The impure sheet is connected with the positive pole of an electroplating dynamo, and the thin sheet of copper is connected with the negative pole. The electrolyte in the tank is a solution of sulphate of copper. The action of the current will cause the pure copper in the impure sheet to disintegrate and it is then carried over and deposited upon the thin sheet, this action continuing until the impure sheet is entirely eaten away. All the impurities which were in the sheet fall to the bottom of the tank.

Other metals are treated in the same way, and this treatment has a very wide range of usefulness.

ELECTROPLATING.--The next feature to be considered in electrolysis is a most interesting and useful one, because a cheap or inferior metal may be coated by a more expensive metal. Silver and nickel plating are brought about by this action of a current pa.s.sing through metals, which are immersed in an electrolyte.